In the process of manufacturing hydraulic cements such as Portland cement, a grinding operation is used to reduce cement particles to relatively smaller particle sizes. A spherical starting material called “clinker,” which essentially consists of hydraulic calcium silicates, calcium aluminates, and calcium aluminoferrite, is mixed with small amounts of gypsum and ground into finely divided particles. As the grinding of clinker to produce the cement consumes substantial quantities of time and energy, it is common practice in the cement industry to employ grinding aids which increase the efficiency of the grinding operation, thereby lowering the power required to grind a unit of cement or alternatively, to increase the output of cement to accommodate high cement demands. The addition of a grinding aid enables the mill to grind the clinker to a smaller size with less energy by prohibiting the buildup of a coating of finer material on the grinding media and walls of the mill by coating the nascent surfaces of the cement clinker.
In U.S. Pat. No. 3,615,785, Moorer et al. disclosed the use of polyglycerols as additives for the grinding manufacture of hydraulic cement, and preferably polyglycerols selected from the group of di-, tri-, and tetraglycerol and mixtures thereof.
The term “glycerol” is often used interchangeably with the terms “glycerin” and “glycerine.” However, more properly speaking, the term “glycerol” applies to the pure chemical compound 1,2,3-propanetriol, while the terms “glycerin” and “glycerine” apply to the purified commercial products normally containing 95% or more of glycerol. A large portion of the commercial supply of glycerin is produced by esterifying fats with methanol in the production of methyl esters. The present inventors believe that such glycerin has been used as an admixture in cement and concrete compositions, but until the present invention glycerin esterified from animal or plant fats has not been used as a grinding aid for cements, cement clinker, or other raw materials used for making cement.
Crude and waste glycerins obtained as a by-product (though not related to biofuel production as in the present invention) have been used previously for cement grinding. One such glycerol blend was described in SU-1604773. A crude polyglycerin derived from fossil fuel processing was previously used by W. R. Grace & Co.-Conn. in grinding aid additive formulations sometime in the 1980's. However, the purity of the glycerin in terms of glycerol level was about 50%, and thus care was needed during formulation with other grinding aid components to prevent sludging. Other uses of glycerin residues, crude glycerins, and waste glycerins in cement applications are described in SU-1271843 and SU-1130548. These materials are believed to contain glycerols of various molecular weights, and most contain salts such as sodium chloride in a quantity up to 15%. The high level of polyglycerins reduces the grinding aid efficiency of crude glycerins obtained from such processes.